Many plastics are provided as blends that include not only plastic resin but also one or more additives that improve the appearance and/or properties of the plastic. For example, in certain electrically conductive blends of polyamide and poly(arylene ether) resins used to fabricate electrostatically painted automotive parts, the electrical conductivity of the blends can be provided by a small amount of carbon nanotubes present as an additive in the blends. In order to improve the uniformity of additive distribution in the plastic and, in some cases, to avoid direct handling of the additive in the final compounding step, the additive is often incorporated into an intermediate plastic composition, known as a masterbatch, and the masterbatch is then combined with other components to form the final plastic composition.
The formation of the masterbatch requires a separate melt blending step that is energy intensive. There is therefore a desire for a less energy intensive means of incorporating additives into plastics, while still preserving the masterbatch's advantages of providing more uniform distribution additive in the plastic and avoiding direct handling of additives in the final compounding step.